Spin polarization of (Ga,Mn)As measured by Andreev spectroscopy: The role of spin-active scattering

Abstract

We investigate the spin polarization of the ferromagnetic semiconductor (Ga,Mn)As by point-contact Andreev reflection spectroscopy. The conductance spectra are analyzed using a recent theoretical model that accounts for momentum- and spin-dependent scattering at the interface. This allows us to fit the data without resorting, as in the case of the standard spin-dependent Blonder-Tinkham-Klapwijk (BTK) model, to an effective temperature or a statistical distribution of superconducting gaps. We find a transport polarization ${P}_{C}\ensuremath{\approx}57%$, in considerably better agreement with the $\mathrm{kP\vec}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{pP\vec}$ kinetic-exchange model of (Ga,Mn)As, than the significantly larger estimates inferred from the BTK model. The temperature dependence of the conductance spectra is fully analyzed.